Wired glass has been in production for many years and in general provides a greater measure of security than ordinary clear or obscure annealed glass. In particular wired glass is widely used as glass balustrading, the wire being effective in preventing people or objects falling completely through the glass when the glass is broken. Wired glass is also used in glass pass doors to act as a barrier for preventing a hand or arm going through the glass accidentally and to hold the glass together longer when exposed to fire and heat. In this latter respect all glass will melt at a high enough temperature. However the wire in the wired glass holds the melting and sagging glass in its original position much longer than unwired glass.
There are three common types of wired glass, namely "Georgian" wired glass which has a square mesh, "Hexagonal" wired glass which has a hexagonal mesh, and "Diamond" wired glass which has a diamond shaped mesh. The wires of the meshes are welded together, e.g. electrically welded together, at their intersecting or cross-over points and are typically made of steel, e.g. chemically treated steel. With "georgian" wired glass the area of each square mesh opening is typically about 155 mm.sup.2 (wires spaced 12.5 mm apart), and the wires typically have a gauge of 0.46 mm. Such wire mesh has good reinforcing properties, improves the fire-resisting properties of the glass and does not obstruct or impair the view through the glass to any great extent.
Known wired glass is generally manufactured by the same basic method of feeding wire mesh into the glass as it passes in a fairly molten state between rollers of a roller system and then cooling the glass to solidify it. However this process is unsatisfactory in three respects. Firstly, the pull on the wire mesh as it is fed into the molten glass distorts the wire mesh so that, with square mesh for instance, the cross wires are not completely straight but become bent. Secondly, the wire mesh tends not to be positioned centrally in he solidified glass. Thirdly the process is costly, especially if the wired glass subsequently has to be further treated, e g. by grinding and polishing to produce "polished plate" glass.
In 1982 the British Standards Institute published BS 6262:1982 relating to codes of practice for glazing for buildings. This standard took recognition of the danger of serious accidents which could occur from ordinary glass when glazed in certain locations and recommends that safety glass or material should be used in these locations, "safety glass" being specified as laminated or toughened glass. A simple laminated glass comprises two sheets of glass bonded together by an interlayer of reinforcing material. The interlayer is able to absorb impact shock and to hold the glass in position when broken or cracked thus preventing spalling of glass fragments and preventing any part of a person's body going through the glass and causing a series injury.
Conventional wired glass was not deemed by the British Standards Institute to constitute a "safety glass" since it was unable to meet their required safety standard. In particular it is unable to retain or hold splinters or slivers of glass brought about by impacting and fracturing wired glass.
In the prior art it is known to incorporate wire in laminated glass to fulfil three differing purposes. Firstly, to render the glass visible by incorporating in the interlayer fine wires running parallel in one direction only at approximately 30 mm centres. Secondly, to provide an electric heater or alarm circuit by incorporating a continuous thin wire filament in the interlayer. Thirdly, to provide a fire-resistant glass in which a conventional wired glass is laminated to another sheet of glass. However such glass is less fire-resistant than ordinary solid (monolithic) wired glass and is considerably more expensive to produce.
It has also previously been proposed in GB-A-2078166 to incorporate a wire mesh in a safety glass, the wire mesh acting as a reinforcement. However the mesh is adhered between two sheets of material to form therewith a sandwich type interlayer and is not therefore truly embedded in the interlayer and does not act to hold the interlayer together if subjected to intense heat, e.g. in a fire. Indeed the action of heat could well cause the interlayer to delaminate.
It is also known from GB-A-2125732 to provide a fine-mesh wire net in a laminated glass to act as a microwave shield. However visibility through the fine-mesh wire net is poor and its presence does not significantly reinforce the glass or assist in rendering the glass fire-resistant.